1. Field of the Invention
The present invention relates generally to control systems for glassware forming machines and in particular to a timing and speed control system which is responsive to the physical properties of the gobs of molten glass.
2. Description of the Prior Art
The individual section glassware forming machine is well known and includes a plurality of sections, each having means for forming glassware articles in a timed predetermined sequence of steps. Typically, the sections are fed from a single source of molten glass which forms gobs of the molten glass. The gobs are distributed to the individual sections in an ordered sequence. The individual sections are operated in synchronism at a relative phase difference such that one section is receiving a gob while another section is delivering a finished glassware article to a conveyor and one or more other sections are performing various ones of the intermediate steps.
The forming means in each section are typically operated from pneumatic motors or actuators. In early prior art machines, the pneumatic motors were controlled by a valve block which, in turn, was controlled by a timing drum driven from a line shaft which synchronized all parts of the machine. The timing drum was later replaced with an electronic control means including a master unit which was responsive to a clock pulse generator and a reset pulse generator, both generators being driven by the line shaft. Such a control system is disclosed in U.S. Pat. No. 3,762,907. Other prior art control systems utilized digital computers with memory and associated program storage for providing a means for programming groups of related functions in accordance with certain boundary events. Such a control system is disclosed in U.S. Pat. No. 3,905,793.
U.S. Pat. No. 4,108,632 discloses an electronic control system utilizing a programmed controller and a pulse generator for generating a real time base for the forming operations. Inputs to the controller are a sensor for detecting the release of the gob from the gob forming means, a temperature sensor for detecting the passage of the gob into the blank station, and a pressure sensor for detecting the start of the parison forming. The controller utilizes the gob release signal to determine the end/start of successive forming cycles, the temperature signal to start the parison forming steps and the pressure signal to determine the duration of the parison forming operation. The speed of the gob forming and releasing is controlled by an electric motor running at a predetermined speed.
A later prior art control system includes a machine supervisory control means connected to a separate section control means for each of the individual sections and to a data storage means. The machine supervisory control means loads each section control means with a control program and timing data from the storage means for forming a specific article of glassware. The machine supervisory control means also obtains the current timing data from each of the section control means at predetermined intervals and sends it to the storage means. Individual forming operation times can be adjusted while the machine is running. Such a control system is disclosed in U.S. Pat. No. 4,152,134.